1. Field of the Invention
This invention relates generally to the field of grain conditioning systems and more particularly to a grain moisture measuring apparatus and method.
2. Description of the Art
Moisture control has always been a factor in milling. Grain purchased from a number of suppliers may have moisture content varying anywhere from 10 to 30 percent of its body weight. In flour milling, such variation in moisture can result in mill chokes or inferior or off-color product. In feed milling, such variation can result in waste due to brittle or improperly conditioned feed. This moisture variation can also vary the energy content of the as-fed ration, which causes variation in animal gain performance. Since the typical mill can process several hundred tons of grain every day, a mill may see fairly rapid swings over a relatively short time in the moisture level of the grain being processed.
To counteract this problem and in order to provide a mill with grain having a more uniform moisture level, grain conditioning systems have been proposed for tempering the grain before it is processed in order to increase its moisture level. A grain conditioning system adds a liquid to the grain as it is loaded into a grain elevator or as it flows into the mill. Typically, grain conditioning systems determine the amount of liquid to be added by measuring the moisture content of the dry (unconditioned) grain, the wet (conditioned) grain, or both dry and wet grain. Systems in which the amount of water added to the grain is determined by measurements of the moisture level of the dry grain are termed feedforward systems. Systems in which the amount of water added is determined not from the dry grain but from the moisture level of already conditioned grain are termed feedback systems. In practice, tempering has been shown to reduce mill stoppages and chokes due to fluctuating mill balance and improve both the efficiency of the milling process and the quality of the end product.
A feed forward system for controlling liquid added to a material such as feed grain during a conditioning process is taught generally by U.S. Pat. No. 5,194,275 to Greer. Greer discloses a feed grain delivery system in which dry grain readings are used to control the amount of moisture added to feed grain in order to raise the moisture content to a relatively constant target level. Since conditioning systems based solely on dry material readings do not measure moisture content in the conditioned product, such feed forward systems are susceptible to variations in the conditioning process due to temperature and changes in water pressure. Variations are also caused due to possible incomplete incorporation of added water into the grain (i.e., incomplete mixing of water and grain). These systems are unable to determine what, if any, effect the conditioning process is having on the material being conditioned and, therefore, cannot adapt to changing conditions.
A feed back system for controlling liquid added to grain during the conditioning process is taught generally in U.S. Pat. No. 3,732,435 to Strandberg, Jr. et al. Strandberg teaches the placement of a moisture sensor at the output of the moisture conditioner. The range at which water is added to or removed from the material is controlled by varying the speed at which the material is exposed to a constant flow of moisture or drying air. In another type of feed back system, a controller is used to adjust the amount of water added to a grain in order to bring the moisture level of the conditioned grain to approximately the target moisture level. U.S. Pat. No. 5,347,468 to Rupp et al. teaches a feed back system for controlling the addition of a liquid to a continuous flow of material and describes an algorithm for controlling the amount of water added during the hydration process.
Since, however, feed back systems do not track the moisture of incoming (dry) grain, they can be confused when wet grain moisture level readings vary due to changes in the dry grain moisture level. Additionally, the ability of feed back systems to track the target moisture level is compromised by the non-homogenized grain samples which have recently been wetted. In other words, the water on the outside and inside of the grain samples differs. The water absorbed by the grain is bound while the water remaining on the outside of the grain is unbound or xe2x80x9cfreexe2x80x9d water. This xe2x80x9cfreexe2x80x9d water is the root cause of erratic electrical characteristics of the grain samples in a feed back system. Furthermore, xe2x80x9cfreexe2x80x9d water on the outside of grain xe2x80x9cblindsxe2x80x9d a capacitance type measurement which tends to show maxed out (invalid) readings with recently wetted samples. In general, xe2x80x9cfreexe2x80x9d water complicates all types of moisture measurement, i.e., infra-red, microwave, or capacitance.
The erratic and unstable electrical characteristics of many materials immediately after the addition of water hinders the ability to obtain accurate, precise measurements of moisture content. Capacitance-type grain moisture measuring devices which treat a grain sample as a dielectric will not generally function properly unless the treated grain has had sufficient time to equilibrate and thus allow surface moisture to penetrate into the grain kernel. Typically, the equilibration times are on the order of hours. Such a time frame is not readily applicable to a grain processing environment where the continuous flow of grain being treated requires nearly instantaneous measurements of grain moisture levels to appropriately condition the grain as it moves through the system. If the treated grain is not allowed sufficient time to equilibrate, the erratic, unstable dielectric properties of the grain make it difficult to accurately measure the moisture level in the recently hydrated material. This instability becomes more apparent as the level of hydration increases. For these reasons, manufacturers will typically restrict a feed back system to use with products which absorb and stabilize moisture rapidly (such as soybean meal and mill feed).
It is apparent that feed back controlled grain conditioning systems, since they operate on the basis of the finished product, should be best capable of reacting to and compensating for changes in grain and water flow conditions. These systems, however, have been limited by their linability to accurately and efficiently measure the moisture level of recently wetted (unequilibrated) grain due to the unstable and erratic electrical characteristics of such materials. Additionally, the cost of such systems are typically higher than other types of systems.
There is a need for an apparatus and method for accurately measuring the moisture of grain as the grain moves through a grain conditioning system. Further, an apparatus and method is needed for accurately and efficiently measuring the moisture level of materials recently wetted to achieve a target level for moisture for the material.
The present invention provides a grain moisture measuring apparatus and method for measuring the moisture content of the grain as the grain moves through a grain conditioning system in which moisture is applied to the grain at a first location. According to one aspect of the present invention, the grain moisture measuring apparatus includes a sample extraction mechanism located at a point downstream from the first location where moisture is applied to the grain. The sample extraction mechanism extracts a sample of grain from the grain moving through the grain conditioning system. A grinding mechanism is connected to the sample extraction mechanism with the grain sample being transferred to the grinding mechanism which then grinds the sample to physically alter the sample. The apparatus further includes a moisture sensor positioned adjacent the grinding mechanism wherein the sample of grain is transferred to a location adjacent the moisture sensor after the grain sample is ground by the grinding mechanism so that the moisture sensor measures the moisture content of the grain sample. Preferably, the moisture sensor is a capacitance-type sensor which provides an electronic signal that corresponds to the moisture content of the grain sample. However, the moisture sensor may be any device that measures grain moisture including but not limited to microwave, infrared. capacitance, chemical, or gravimetric sensors.
According to another aspect of the present invention, a method is provided for measuring the moisture content of grain as the grain moves through a grain conditioning system in which moisture is applied to the grain at a first location. The method includes the step of extracting a sample of grain from the grain moving through the grain conditioning system at a point downstream from the first location where moisture is applied to the grain. Further steps include grinding the sample of grain to physically alter the sample and measuring the moisture content of the grain sample after the grain sample has been ground.
Pursuant to another aspect of the present invention, a grain conditioning system for conditioning a continuous flow of grain to a target moisture level is provided which incorporates the moisture measuring apparatus of the present invention. Such an apparatus includes a fluid control valve connected to a sprinkler head where the fluid control valve is capable of being set to a desired liquid flow rate in order to control the flow of a liquid to the sprinkler head. The apparatus further includes an auger positioned to convey grain past the sprinkler head in order to condition the grain. A sample extraction mechanism is located at a point downstream from the sprinkler head so that the sample extraction mechanism exacts a sample of grain from the grain moving through the auger. A grinding mechanism is connected to the sample extraction mechanism such that the sample of grain extracted from the sample extraction mechanism is transferred to the grinding mechanism and the grinding mechanism grinds the grain sample to physically alter the grain sample. A moisture sensor is positioned adjacent to the grinding mechanism with the sample of grain being transferred to a location adjacent the moisture sensor after the grain sample is ground by the grinding mechanism such that the moisture sensor measures the moisture content of the grain sample and provides a first electronic signal that corresponds to the moisture content of the grain sample. The apparatus further includes a processor connected to the fluid control valve and the moisture sensor wherein the processor receives the first electronic signal from the moisture sensor that corresponds to the moisture content of the grain sample and the processor creates an output control signal which controls the operation of the fluid control valve so that the fluid control valve permits a desired liquid flow rate that corresponds to the output control signal from the processor so that the moisture level of the conditioned grain approximates the target moisture level.